Intramammary infections and somatic cell counts in meat and pelt producing ewes with clinically healthy udders

Abstract

Mastitis in sheep is common and is important both from an economic and from a welfare point of view. It can be either clinical or subclinical, bacterial or, more seldom, lentiviral. There are no data on the national prevalence of subclinical mastitis (SCM) or intramammary infection (IMI), and causative pathogens, in ewes in Sweden.Diagnosis of SCM and/or IMI is based on inflammatory indicators, measured in milk and additional bacteriology. Somatic cell count (SCC) is the most widely used indicator of SCM and/or IMI and can be measured either directly or indirectly with e.g. California Mastitis Test (CMT). However, the use of SCC as an indicator for mastitis and/or IMI in ewes is not fully evaluated, especially not in meat- and pelt producing herds. The aim of this study was therefore to investigate the prevalence of IMI and bacterial panorama in ewes with clinically healthy udders, in meat- and pelt producing herds in Sweden. Moreover, we wanted to define a cut-off for SCC and CMT for detecting ewes with IMI that would be suitable for use under field conditions.Udder half milk samples (n=2134) were collected at weaning and lambing from meat- and pelt producing ewes (n=773), in 22 farms in Sweden. Only clinically healthy animals were included in the study. Milk samples were analysed for bacteriology and SCC and were given a CMT score.Intramammary infection was found in 30% of the ewes and in 14% of the udder half milk samples. No bacteria were found in 74% of the milk samples, and mixed flora was found in 12% of the samples. Among the 287 milk samples where IMI was identified, coagulase negative staphylococci (CoNS) were most prevalent (58%) followed by Staphylococcus (S.) aureus (9%) and Mannheimia (M.) haemolytica (6%). Among the 165 CoNS findings S. simulans was the most common (26%), followed by S. warneri, S. equorum, S. xylosus, S. haemolyticus and S. chromogenes. A CMT score of ≥3 and a SCC of ≥500,000 cells/ml at weaning or CMT score ≥3 and a SCC of ≥400,000 cells/ml after lambing gave the highest possible Se at the same time as the highest possible Sp for identifying udder halves with IMI and may be used for screening for IMI in Swedish meet and pelt producing herds.To conclude, one third of Swedish meat- and pelt producing ewes without clinical signs in the udder had IMI in one or both udder halves at weaning and or after lambing, and CoNS was the most common bacterial finding. A high SCC (≥400,000–500,000 cells/ml) was associated with IMI and a difference in having a high (CMT 3–5) or low (CMT 1–2) between udder halves can be used as an indicator of IMI under field conditions.